I think you missed what he was saying. He was saying that there is a gap in time between scientists choosing to focus on something and the accumlation of evidence that makes them feel it is real. He is saying that, therefore, even in science, it is clearly acknowledged that real things do not yet have empirical evidence for them or what would be the point of many specific kinds of research. Like looking for a new particle, for example, or seeing if in fact there are so far unseen species high up in the jungle canopy that are nowhere else.
Or to put this in the negative. It would be unscientific to say things do not exist only because there is no evidence for them. So many fruitful projects and of course many (nevertheless possibly useful) duds would never have been carried out.